Method for production of porous semi-products from aluminum alloy powders

ABSTRACT

The invention relates to powder metallurgy and can be used for producing porous materials having high thermal and sound insulation and energy absorption combined with light mass, incombustibility and the ecological cleanness thereof. According to said invention, during mixing a powder of an aluminum alloy with porophores, the powders of aluminum oxide and aluminum hydroxide ranging from 1 to 10% and crushed particles of secondary aluminum alloys of the dimensions ranging from 0.5 to 4.5 mm are added to the powder mixture. The particles are mixed in an atrittor until a mechanically alloyed powder alloy is obtained. The powder mixture being heated, it is poured in a vertical container which vibrocompacts the mixture and maintains the temperature thereof. Afterwards, said mixture is transferred to the rectangular groove of a rolling mill in order to carry out a continuous hot compaction in a dead groove of horizontal rollers at a temperature ranging from 430 to 500° C. according to the following condition: H=h×γ×a, where H is an opening between rollers along the arc of contact in mm, h is the thickness of the produced sheet, γ is a compaction ratio of the powder, a is an experimental ratio equal to 1.5=a=4.5. Said invention reduces production cost by using aluminum alloy refuses, expanding the range of sheets and plates and increases the efficiency of the production thereof.

FIELD OF THE INVENTION

[0001] The invention relates to the field of powder metallurgy and canbe used for producing porous materials showing a number of uniqueproperties such as good thermal and sound insulation and energyabsorption in combination with light weight, incombustibility andabsolute environmental safety. Material with this set of physical andmechanical properties can be used for production of components forbuilding machinery, road construction, motor-vehicle industry, aircraftindustry and other branches of industry wherein combination of theseproperties can be desired.

[0002] The method comprises mixing of powders of an aluminum alloyselected from the group consisting of Al—Si—Cu—Mg, Al—Cu—Mg—Si,Al—Mg—Si, Al—Mg—Cu—Si (cast alloys), Al—Cu—Mg—Mn, Al—Mg—Cu, Al—Zn—Cu—Mg,Al—Zn—Mg—Cu (wrought alloys), which contain surface aluminum oxide(0.5-1.5 wt %) formed during atomization, with powders of Al₂O₃ andaluminum hydroxide ranging from 1.0 up to 10 wt % and active porophoreTiH₂ from 0.5 up to 1.2 wt % showing a decomposition temperature abovethat of powder aluminum alloy matrix melting, or mixing of crushed scrapparticles of certain wrought, aluminum alloys which meet requirementsspecified for AM

, A

31, A

33, AM

3, AM

5,

16 and cast alloys (scrap particles being 0.5-4.5 mm in size) with amixture of aluminum oxides and porophore by mechanical alloying.Addition of aluminum oxide together with aluminum hydroxide ranging from1.0 up to 10% both in aluminum powder and in mixed crushed scrap ensuresa noticeable increase in viscosity of melt. The powder mixture ormechanically alloyed mixture produced in an attrittor is fed as auniform layer on a conveyer of a heating furnace. Heating of saidmixtures is carried out in nitrogen atmosphere (dew point is −40° C.) ina temperature range from 450 up to 600° C. under an excessive pressurefrom 10 up to 100 mm H₂O. Each heated powder mixture is poured in aloading bin of a vertical rectangular chute wherein the preheatedmixture is uniformly compacted due to vibration and transferred from topdownwards. Cooling-down of said mixture during transportation in thevertical rectangular chute is prevented as it gets through a heatingfurnace wherein the desired temperature is maintained in a range of450-600° C. depending on powder alloy composition and other processparameters. Travel speeds of said mixture on the conveyer of thepreheating furnace and in the vertical chute are the same. From thefunneled opening of the chute the heated mixture is fed to a rollingmill with rolls arranged horizontally and each of them has an internalturned groove with a depth equal to a half of a thickness of ahot-compacted semi-product to be produced from said powder mixture. Achosen rolling speed or speed of pulling the hot powders in a hotcompaction zone between the rolls should be in agreement with that ofpowder transportation by means of the vertical vibrating chute and withthat of powder transportation on the conveyer in case of powderpreheating in the furnace under nitrogen atmosphere. Side ridges of theturned grooves of each roll touch each other and thereby create closerectangular space which forms final sizes of a compacted sheetsemiproduct produced from the powder mixture. The side ridges of therolls confine transverse movement of powder particles when they fallwithin a field of forces applied vertically in a closed space. Creationof the stringent closed space in the force application area of the yieldelongation zone results in a change of the scheme of the stress-strainedstate. Namely, the scheme of the stress-strained state, in case ofrolling with the use of the smooth rolls, ensures deformations in threedirection: the most intensive deformation in the rolling direction andslight deformation in the transverse direction, which causes widening ofthe sheets during rolling. In case of the use of the grooved rollsforming a closed groove, under certain conditions of powder feeding,proposed by the present invention, conditions for formation of thestress-strained state corresponding to extrusion with the unidirectionaldeformation vector, as in case of hot extrusion on a hydraulic press,are created, i.e. plastic deformation develops in the direction of themain deformation vector. Under certain conditions proposed by thepresent invention, hot compaction of the powder mixture can be carriedout between the rolls of the rolling mill to obtain a relative compactdensity up to 0.97-0.99% and to produce a hot-compacted continuous stripor sheet from 150 up to 1500 mm in width and from 3 up to 15 mm inthickness.

[0003] Conditions of formation of a continuous hot-compacted orhot-extruded flat sheet semiproduct between the special rolling millrolls which form a closed space of a powder rolling mill can bedescribed by the following equation: H=h×γ×α, where:

[0004] H is an opening between the rolls along the arc of contact, mm;

[0005] h is a thickness of the compacted sheet, mm;

[0006] γ is a compaction coefficient

[0007] α is an experimental coefficient, where 1.5≧α≧4.5.

[0008] As a result of application of forces close to volume-stressedstate in the yield elongation zone and at a temperature of 450-500° C.,active interactions of powder mixture particles or particles develop.Powder particles drawing together by forces undergo partial destructionof oxide films, which is accompanied by formation of juvenile surfaces,or direct convergence when the oxide film is particle-particleinterface. As a result of a temperature and by forces in the yieldelongation zone, due to active diffusion, new strong metallic bondingsare generated between powder particles both in contact areas with purejuvenile surfaces and in contact areas with metallized oxide film. Thesestrong metallic bondings can sustain noticeable tensile stresses in caseof the change of stress-strained state and transition from hotcompaction to hot extrusion in the rolling mill when a continuous sheetwith a preset thickness is produced. The hot compacted sheet produced iscut to blanks. Such blanks are placed in forms lateral side of which aremade from heat-insulating material. The degree of blackness of thismaterial is noticeably differed from that of aluminum. Bottoms of theforms are made from a refractory steel sheet or a net with small mesh.The form, on the one hand, is a transport means in which the blank isfed for heat treatment, and, on the other hand, it creates athermostating space for the blank heated during heat treatment.High-temperature heat treatment is carried out by heating of the blankabove a temperature of solid-liquid phase transformation. Termination ofthe foaming process is determined visually, when contrast aluminum edgeappears above the form wall. The form is taken out of a furnace, itssurface is cooled down and the foaming is arrested at the desiredheight.

[0009] The technical result obtained due to realization of the inventionincorporates high output, creation of waste-free production, lowproduction costs of commercial porous sheet semiproducts due to the useof scrap or secondary aluminum alloys both in case of production ofatomized powder and in case of production of grinded particles ofcertain aluminum alloys with subsequent milling in the attritor forproduction of the mixture with desired chemical composition.

[0010] The invention relates to the field of powder metallurgy and canbe used for producing porous semiproducts for building machinery, roadconstruction, motor-vehicle industry, aircraft industry and otherbranches of industry wherein combination of unique properties of thismaterial, such as isotropy of properties, energy absorption, thermal andsound insulation, light weight, buoyancy and absolute environmentalsafety are desired.

BACKGROUND OF THE INVENTION

[0011] Already known in the prior art, there is a method for productionof porous semiproducts from powder alloys based on aluminum and copper,that incorporates mixing of alloy powder with a porophore, filling ofthe mixture in a press container, simultaneous heating of the filledcontainer and applying pressure at which the porophore does notdecompose, simultaneous cooling and release of the pressure,disassembling of the container followed by pushing of the solidbriquette out of it, which is immediately heat treated to produce aporous body or is subjected to preliminary hot deformation via extrusionand subsequent rolling for production of sheets which are cut to lengthand heat treated (German patent No. 4101630, B 22 F 3/18, B 22 F/24,1991).

[0012] Limitation of this method is a very small range of semiproductsin terms of sizes and shape, which can be produced by this method asweight of the briquette is 2-5 kg. In addition, this method shows a verylow output because of the prolonged heating of the large size presscontainer filled with the powder mixture. Even in the case where thepowder mixture would be heated in a container of 100 mm in diameter and400 mm in height, the heating operation would be unprofitable.

[0013] Also known, there is a method for production of poroussemi-products, which incorporates several variants for production ofcompact briquettes followed by rolling for sheet production. However incases of all variants of this method, mixing of a metallic powder withat least one powder, porophore, is the main and common operation.

[0014] The first variant includes placement of porophore-free metalliclayer on the bottom floor of a press container, covering of the metalliclayer with a powder mixture containing a porophore and then covering ofthe powder mixture with the second metallic layer. After heating of thecontainer wherein the filled powder mixture is between two installedplates hot compaction is carried out. This operation completes themethod. The hot-compacted shape of a body produced can be changed viasubsequent hot rolling for formation of a new body wherein a high-porousfoamed metallic layer appears between two metallic layers.

[0015] The second variant includes installation of a large-size solidmetal disc in an empty press container (extrusion tooling) and fillingof the container space with a powder mixture containing a porophore.Then, the container with the powder mixture is subjected to heatingfollowed by application of a pressure of about 60 MPa. Due to theapplied pressure, the central part of the hard metallic disc whichblocks the press die hole begins flowing through this hole and ensuresextrusion process. During subsequent extrusion stages the compactedpowder mixture plastically deforms and flows through the die hole also.In this case the hard metal covers the extruded powder mixture whichable to foam under the hard metallic layer. Then, the hot-extruded cladstrip is rolled in sheet. The hot-rolled sheet is cut to blanks andsubjected to heat treatment. After foaming of this combined body themetallic layer covers a core consisting of high porous foam.

[0016] The combined hot-compacted and hot-extruded briquettes producedvia both variants of the method should be further subjected to hotrolling for production of sheets or plates. Due to a heat treatmenttemperature the powder core is transformed in a porous metallic body(U.S. Pat. No. 5,151,246. September, 1992. B 22 F 3/18, B 22 F 3/24).

[0017] Also known in the prior art, there is a method for production ofporous semi-products with the usage of reusable split cans. The methodincludes filling of a mixture of aluminum and copper powder (from 1 upto 10%) with a porophore in these cans, sintering of the mixture in aninert gas flow in the split can, pushing of the hot solid briquette in apress container for subsequent extrusion to produce a bar. The bar witha clad layer or without it is cut to length and is rolled to sheets ofcommercial sizes and then heat treatment is carried out for productionfoamed aluminum (Patent RU No. 2121904 of Nov. 20, 1998, B 22 F 3/11).

[0018] In spite of some advantages in comparison with the above method,said method has a number of limitations peculiar to it, namelyinadequate output and product yield, that results in an increasedproduction costs of semiproducts.

[0019] Said method and the above one are the most similar analogues(phototypes) in terms of the set of properties.

[0020] Limitations of this method as well as all the above methods arelimited possibility of production of semi-products, especially sheets ofcommercial sizes, low product yield and output, high production costs.Low product yield is attributed to formation of large amount of scrapduring extrusion (butt-ends, head and back ends) and during rolling(side crops and back end crops).

[0021] The purpose of the present invention is production of continuoushot-compacted or hot-extruded sheets of commercial sizes by means ofdirect hot compaction or hot extrusion of a mixture of powders ofvarious chemical composition with a porophore or a mixture of coarseparticles of 0.5-4.5 mm in size with a porophore mechanically alloyed inan attritore and also of grinded particles of certain aluminum alloys ina rolling mill.

[0022] The task of the invention is a noticeable improvement in output,product yield up to 95-97%, a reduction in production costs due to theuse of aluminum alloy scrap, widening of a range of sheets and plateswith an increase in sheet area up to 2.5-3% square metres.

[0023] The most similar analogue of the invention is a method forproduction of porous semiproducts and aluminum alloy powders. The methodincludes mixing of an aluminum alloy powder with a porophore showing adecomposition temperature above that of aluminum alloy powder melting,with addition of a copper powder from 1 up to 10%, filling of thismixture in a mould, heating of this mould filled with the powdermixture, pushing of the hot mixture in a press container, hot extrusionfor production of a solid briquette, cooling, hot deformation, forexample, rolling, cut of a rolled sheet to length, placement of theblanks produced in forms with heat-insulating material walls andsubsequent high temperature treatment for conduct of forming process ata liquidus temperature of the powder alloy. In this case, alloys ofAl—Cu—Mg, Al—Zn—Cu—Mg, Al—Zn—Mg, Al—Mg or Al—Si—Cu—Mg systems are usedas powder aluminum alloys and nitrogen or argon are used as inert gasesduring heating of the powder mixture. For production of clad stripheating of the powder mixture is carried out in the mould whereinaluminum disc is placed on the bottom (RU 2121904, Nov. 20, 1998, B 22 F3/11).

[0024] The common signs of the known method and this invention aremixing of an aluminum alloy powder with porophores showing adecomposition temperature above that of aluminum alloy powder melting,filling of the mixture in a mould, heating of the mould in an inert gasatmosphere, hot compaction, extrusion, cutting-to-length, hot rolling tosheets, cutting of the sheets to blanks, placement of them in a formwith heat-insulating material walls, subsequent high temperaturetreatment for conduct of foaming process at a liquidus temperature ofthe powder alloy and cooling.

DESCRIPTION OF THE INVENTION

[0025] The method of the present invention differs from the prior art bythe fact that during mixing of an aluminum alloy powder with porophores,oxide and hydroxide aluminum powder additions from 1.0 up to 10% aremade in the mixture or porophores to be added and aluminum oxides aremixed with coarser aluminum alloy particles from 0.5 up to 4.5 mm insize in an attritor to produce mechanically alloyed powder alloy, afterheating the various powder mixtures are filled in a mould installedvertically which ensures simultaneous vibratory compaction andmaintenance of a temperature of the powder mixture, and hotconsolidation (compaction or extrusion) is carried out by feeding of thepowder mixture in the grooved horizontal rolls of a rolling mill at atemperature of 430-500° C. provided that the following conditions areobserved:

H=h×γ×α, where:

[0026] H is an opening between the rolls along the arc of contact, mm;

[0027] h is a thickness of the compacted sheet, mm;

[0028] γ is a powder compaction coefficient;

[0029] α is an experimental coefficient, where 1.5≧α≧4.5.

[0030] The present invention concerns a method for production of poroussemi-products from aluminum alloy powders comprising the steps of:

[0031] I) Mixing of powders of an aluminum alloy selected from the groupconsisting of Al—Cu—Mg—Mn, Al—Si—Cu—Mg, Al—Cu—Mg—Si, Al—Mg—Si,Al—Mg—Cu—Si (cast alloys), Al—Cu—Mg—Mn, Al—Mg—Cu, Al—Zn—Cu—Mg,Al—Zn—Mg—Cu (wrought alloys) with addition of a mixture of aluminumoxide and aluminum hydroxide ranging from 0.5 up to 10 wt % and activeporophore TiH₂ ranging from 0.5 up to 1.2 wt % showing a decompositiontemperature above that of powder aluminum alloy matrix melting or mixingof coarse particles of crushed scrap of certain wrought aluminum alloysAM

, A

31, A

133, AM

3, AM

5,

16 and other cast alloys (scrap particles being 0.5-4.5 mm in size) witha mixture of aluminum oxide and a porophore in an attritore by themechanical alloying technique.

[0032] II) Feeding of the powder mixture of step I as a uniform layer ona conveyer of a heating furnace. Heating of the mixture in nitrogenatmosphere at a temperature range of 450-600° C. under an excessivepressure from 10 up to 100 mm H₂O;

[0033] III) Feeling of the pre-heated mixture of step II in a loadingbin of a vertical chute wherein the pre-heated mixture is uniformlycompacted due to vibration and transferred from top downwards;

[0034] IV) Filling of the pre-heated mixture of step III in a heatingfurnace wherein the desired temperature is maintained in a range of450-600° C. depending on powder alloy composition and other processparameters to prevent cooling-down of said mixture during transportationon the chute; travel speeds of said mixture on the conveyer of thepreheating furnace and in the chute are the same;

[0035] V) Feeding of the pre-heated mixture of step 1V from the funneledopenting of the chute to a rolling mill with horizontal rolls, with eachroll having an internal turned groove which depth is equal to a half ofthickness of a hot-compacted sheet semiproduct to be produced. A chosenrolling speed or speed of pulling said pre-heated mixture in a hotcompaction zone should be in agreement with that of pre-heated mixturetransportation by means of the vertical vibrating chute and with that ofpowder transportation on the conveyer in case of powder preheating inthe furnace under nitrogen atmosphere of step II. Side ridges of theturned grooves of each roll touch each other and thereby create closerectangular space which forms final sizes of a hot-compacted sheetsemiproduct produced from said powder mixture. The side ridges of therolls confine transverse powder particle movement by rolling forces.Creation of the stringent groove in the force application area of theyield elongation zone results in a change of the scheme of thestress-strained state. Namely, the scheme of the stress-strained state,in case of rolling with the use of the smooth rolls, ensuresdeformations in three directions: the most intensive deformation in therolling direction and slight deformation in the transverse direction,which causes widening of the sheets during rolling. In case of the useof the grooved rolls, proposed by the present invention, which form aclosed groove under certain conditions, conditions for formation of thestress-strained state corresponding to extrusion with the unidirectionaldeformation vector, as in case of extrusion, are created, i.e. plasticdeformation develops in the direction of the main force vector. Undercertain conditions proposed by the present invention hot compaction ofsaid powder mixture can be carried out between the rolls of the rollingmill to obtain a relative compact density up to 0.97-0.99% and toproduce a hot-compacted continuous strip or sheet from 50 up to 1500 mmin width and from 3 up to 10 mm in thickness.

[0036] Conditions of formation of a continuous hot-compacted orhot-extruded flat sheet semiproduct between special rolling mill rollswhich form a closed groove in the rolling mill can be described by thefollowing equation:

H=h×γ×α, where

[0037] H is an opening between the rolls along the arc of contact, mm;

[0038] h is a thickness of the compacted sheet, mm;

[0039] γ is a powder compaction coefficient;

[0040] α is an experimental coefficient, where 1.5≧α≧4.5.

[0041] As a result of application of forces close to volume-stressedstate in the yield elongation zone and at a temperature of 430-500° C.,active interactions of powder mixture particles develop. Powderparticles drawing together by forces undergo partial destruction ofoxide films, which is accompanied by formation of juvenile surfaces, ordirect convergence when the oxide film is particle-particle interface.As a result of a temperature and by forces in the yield elongation zone,due to active diffusion, new strong metallic bondings are generatedbetween powder particles both in contact areas with pure juvenilesurfaces and in contact areas with metallized oxide film. These strongmetallic bondings can sustain noticeable tensile stresses in case offormation of a continuous dense hot-extruded sheet with a presetthickness. The hot-compacted or hot-extruded sheet produced is cut toblanks which are placed in forms lateral sides of which are made fromheat-insulating material. The degree of blackness of this material isnoticeably differed from that of aluminum. Bottoms of the forms are madefrom a refractory steel sheet or net with small mesh. The form, on theone hand, is a transport means in which the blank is fed to heattreatment and, on the other hand, it creates a thermostating space forthe blank heated during heat treatment. High-temperature heat treatmentis carried out by heating of the blank above a temperature ofsolid-liquid phase transformation. Termination of the foaming process isdetermined visually, when contrast aluminum edge appears above the formwall. The form is taken out of furnace, surface is cooled down and thefoaming is arrested at the desired height.

[0042] In addition, in the particular case of realization of the method,after termination of the foaming process the form with heat-insulatingmaterial walls is placed in a technological space of a furnace withlower temperature and for formation of upper smooth surface, a smoothheat-insulating material plate which does not react with aluminum is puton the end of the form. Then the form is taken out of the furnace, theplate is taken away and the upper smooth surface of the semiproductproduced is cooled down intensively.

[0043] In addition, in the particular case of the realization of themethod, the heat-insulating material plate which does not react withliquid aluminum is made with embossed surface which forms a replicatedimpression on the solidifying aluminum surface.

[0044] In addition, in the particular case of the realization of themethod, prior to high-temperature treatment, a stamped sheet is placedon the bottom of the form, and the blank is placed on said sheet. Afterplacement of said form in a technological space of the furnace withlower temperature the heat-insulating material plate which does notreact with molten aluminum and made with embossed surface is put on theend of the form to produce replicated impression on the upper aluminumsurface. Then the form is taken out of the furnace, the plate is takenaway and the upper surface of the semiproduct produced is cooled downintensively.

[0045] In addition, in the particular case of the realization of themethod, for aluminum powder use is made of grinded scrap of aluminumalloy semiproducts both extruded and rolled ones, made from softaluminum alloys A

O, A

1 and wrought alloys AM

, A

31, A

33, AM

3, AM

5,

16, as well as copper, plastic metals and alloys, with particle sizebeing from 0.5 up to 4.5 mm.

[0046] In addition, in the particular case of the realization of themethod, in case of mixing of an aluminum alloy with porophores in theattritor, use is made of grinded particles of aluminum alloys and copperand other plastic metals with size fractions of 0.5-2.5 mm, 1.0-3.0 mm,1.5-4.5 mm.

[0047] In addition, in the particular case of the realization of themethod, when grinded scrap of aluminum alloys A

O, A

1 and hard wrought alloys AM

, A

31, A

33, AM

3, AM

5,

116 are mixed in the attritor, additions of a porophore are madetogether with additions of refractory particles of aluminum oxide, boroncarbide and silicium carbide with a range of size being 5-100 μm.

[0048] In addition, in the particular case of the realization of themethod, when grinded scrap of aluminum alloys is mixed in the attritor,additions of refractory intermetallics particles, for example, N, Al₃,NiAl, Cr₂Al₆ with a range of size being 10-100 μm are made in themixture.

[0049] In addition, in the particular case of the realization of themethod, for a reduction in thickness of a sheet to be produced duringhot compaction, the powder mixture is fed between moving steel sheetspassed by the vibrating chute in the grooved rolls of the rolling mill.

[0050] In addition, in the particular case of the realization of themethod, during hot compaction of the powder mixture, cladding of thecompact with steel or titanium sheets can be carried out due to feedingof the powder mixture between the moving hot sheets passed by thevibrating chute in the grooved rolls of the rolling mill with subsequentfolding of ends of the sheets for formation of a seam. In this casealso, some proportions for filling of the powder mixture are specifiedand a temperature of the powder mixture in the yield elongation zoneshould be increased up to 500-520° C., with degree of deformation being2-5%.

[0051] In addition, in the particular case of the realization of themethod, during hot compaction of the powder mixture, cladding of thecompact with aluminum sheets can be carried out due to feeding of thepowder mixture between the moving hot sheets passed by the vibratingchute in the grooved rolls of the rolling mill with subsequent foldingof the ends of the sheets for formation of a seam. In this case also,some proportions for filling of the powder mixture are specified and atemperature of the powder mixture in the yield elongation zone should bemaintained up to 430-450° C.

[0052] In addition, in the particular case of the realization of themethod, when the foaming process is carried out, it is possible todetermine termination of the process visually and objectively due to adifference in the degree of blackness of the form wall and aluminum andappearance of light belt of aluminum above the form wall.

[0053] The possibility of replication of the invention characterized bythe above-mentioned set of signs and the possibility of the realizationof the purpose of the invention can be corroborated by the descriptionof the following examples.

EXAMPLE 1

[0054] The example of the realization of the method for production offlat porous semiproducts is as follows.

[0055] Al—Mg—Cu—Mn aluminum alloy powder (a liquidus temperature of thealloy is 640-645° C., a temperature of low-melting point non-equilibriumeutectic is 535-540° C.) of 500 kg in weight was mixed with TiH₂porophore (a decomposition temperature is 690° C.) of 5.4 kg in weightand with a mixture of Al₂O₃ and Al₂O₃ (H₂O) of 12.5 kg in weight andfilled in a bin. Then, using a special measuring machine, the powdermixture was spread on a belt conveyer of the heating furnace as auniform layer with a bulk weight of 1.23-1.32 g/cm³. The powder mixturewas heated in the furnace under nitrogen atmosphere at a temperature of500° C. The heated powder mixture was fed in a receiving funnel of thevertical rectangular chute joined up with a vibrating system whichserves for pre-compaction of said powder mixture to obtain a density of1.6-1.8 g/cm³ and transportation of the powder from top downwards. Thevertical chute traverses the furnace for heating of the powder mixtureand maintenance of the desired temperature up to 500° C. Then, from thefunneled opening of the chute the hot pre-compacted powder mixture isfed in a receiving bin of the rolling mill with a design opening betweenthe rolls and a preset rolling speed. The critical specified parameteris a rolling speed or speed of pulling the hot powder in the hotcompaction zone with an opening of 6 mm. All other plant items whereinthe powder mixture is transported ensure synchronous continuous feedingof said mixture to the rolling mill and maintain regularity of volume,weight and temperature variables of the production process. When the hotpowder mixture is fed in the closed space of the yield elongation zoneat a temperature of 430-450° C. and under a specific pressure from 300up to 600 MPa, hot compaction takes place (relative density is0.98-0.99). A 400 kg sheet was continuously produced in the rollingmill. The hot-compacted sheet was cut to length on shears behind therolling mill. Some first hot-compacted blanks were fed for free foaming.These blanks were placed in the forms, sizes of which corresponded tothose of the blanks, with walls made of heat-insulating material andwere subjected to high-temperature treatment. When a temperature of ahot-compacted blank exceeded that of solid-liquid phase transformation,the foaming of this powder blanks began and when aluminum layer appearedabove the form wall of 27 mm in height, termination of the foaming wasevaluated visually. The form was taken out of the furnace and the foamedblank was cooled down intensively. Sizes of the porous semiproductsproduced corresponded to those of the form. Bottom surface of the poroussheets was smooth, while the top surface had indications of swellsbecause of internal pores. Side surfaces of the foamed plate weresmooth. Density of the porous plates produced was 0.58-0.61 g/cm³.Porous semiproduct yield was 100%.

[0056] The second part of the hot-compacted blanks of 1000×120-200×6 mmin size was foamed in the same heat-insulating material forms at atemperature of 760° C. and after appearance of aluminum edge above theform wall of 27 mm in height termination of the foaming process wasevaluated visually. The form was transferred from the furnace in itstechnological space with lower temperature, wherein the plate with asmooth surface was put on the end of the form and after fixation of thesmooth surface the plate was taken away, the form was taken out of thefurnace and the foamed semiproduct was cooled down intensively. Size ofthe porous semi-products produced was 1000×120-200×27.5 mm. In thiscase, top and bottom surfaces of the porous plates were smooth. Sidesurfaces of the foamed plates were smooth as well. Density of the poroussemiproducts was 0.60-0.63 g/cm³. Porous semiproduct yield was 100%.

[0057] The production process offered by the present invention isdeveloped in such a way that process scrap is practically absent. Onecan see that the main operation, namely hot compaction between the rollsof the rolling mill should not form scrap by its nature. Heating of thepowder mixture under nitrogen atmosphere and feeding of said heatedmixture in the rolling powder mill are scrap-free operations also. Onlyin case of hot compaction, edges can be slightly teared but they shouldbe trimmed. Some small amounts of the scrap in the form of trimmed edgesof the hot compacted sheets are grinded and recycled in the powdermixture. The optimized production process of foaming of the densehot-compacted sheets in the heat-insulating material forms offers highproduct yield. Therefore, said final product yield of 95-97% correspondsto the real value.

[0058] The effect of a temperature of the powder mixture heating priorto hot compaction between cold rolls of the rolling mill should bediscussed specifically. If heating of the powder mixture is carried outat temperatures below 450° C., intensive cooling of the powder mixturein the yield elongation zone results in both a sharp increase in forcesapplied to the rolls and a retardation of diffusion processes. As aresult, hot compaction of the mixture does not take place and a sheetstructure is brittle and porous (relative density is 0.80-0.85) bodywhich is not applicable for foaming.

[0059] If heating of the powder mixture is carried out at temperaturesabove 600° C., overheating results in formation of low-melting pointeutectics and appearance of large amounts of liquid phase insideoxidized particles and, thereby, loss of flow ability of the powdermixture. For TiH₂ porophore particles the overheating above 600° C. isadverse to the most extent as it accelerates decomposition of TiH₂porophore, results in loss of a noticeable fraction of hydrogen in theporophore and reduces its future activity during foaming of thehot-compacted sheet. The first source of hydrogen liberation isdecomposition of TiH₂ at a heating temperature. The second one issurface hydrogen formed due to reaction of interaction between sorbedH₂O molecules and aluminum cations which diffuse through oxide films.Hydrogen liberated during heating of TiH₂ and surface hydrogen liberatedinto the conveyer furnace space increase hydrogen concentration andcreate certain hazard in case of heating of the powder mixture.

[0060] Organization of safe production process calls for creation ofnecessary conditions for accident prevention. Therefore, heating of thepowder mixture is carried out in the conveyer furnace under nitrogenatmosphere with an excessive pressure from 10 up to 100 mm H₂O, thatexcludes the possibility of ingress of oxygen in the powder mixtureheating zone.

[0061] Heating up to temperatures of 450-500° C. is not critical foratomized powders in terms of formation of low-melting point eutectics.As the atomized powders have a non-equilibrium structure, formation oflow-melting point eutectics is shifted to a zone of higher temperaturesby 20-30° C. Overheating up to 500-550° C. has certain risk of formationof low-melting point eutectics, however, due to close contact with thecold rolls of the rolling mill liquid eutectic solidifies and ensures,thereby, high properties of the hot-compacted sheets. Heating up to500-550° C. is recommended only at an initial stage of the process. Thisoverheating created artificially caries a large reserve of heat energyin the bulk of the powder under compaction and in spite of the fact thatthe rolls of the rolling mill are cold, a temperature of the powder inthe yield elongation zone does not reduce below 450° C. The use ofhigher rolling rates favours maintenance of a powder mixture temperatureand simultaneously results in heating of rolling roll surfaces. Heatingof the roll surfaces up to a temperature of 100-150° C. allows one toreduce a temperature of heating of the powder mixture in the conveyerfurnace with nitrogen atmosphere and in the furnace for maintenance of atemperature during transportation of the powder mixture in the verticalchute.

[0062] Correction of a temperature in the direction of its reductiondown to 450-500° C. at initial stages of heating of the powder mixtureresults in a noticeable reduction in intensity of TiH₂ porophoredecomposition and maintains a compaction temperature within a range of430-450° C.

EXAMPLE 2

[0063] The example of the realization of the method for production offlat porous-semiproducts with the use of grinded particles of certainsecondary aluminum alloys is as follows.

[0064] Aluminum alloy particles of 0.5-4.5 mm in size, produced bygrinding of

16 alloy scrap (a liquidus temperature of the alloy is 640-645° C., atemperature of formation of equilibrium low-melting point eutectic is505-510° C.) of 300 kg in weight were mixed in the water-cooled attritorunder nitrogen atmosphere with additions of TiH₂ porphore of 3.25 kg inweight (a decomposition temperature is 690° C.) and mixtures of Al₂O₃and Al₂O₃ (H₂O) of 10.5 kg in weight to produce

16 mechanically alloyed alloy with uniform distribution of porophore andaluminum oxides particles added to the alloy. This

16 alloy-based mechanically alloyed powder was filled in a bin. Then,using a special measuring machine, the powder was spread on a beltconveyer of the heating furnace as a uniform layer with a bulk weight of1.35-1.41 g/cm³. The powder was heated in the furnace under nitrogenatmosphere at a temperature of 500° C. The heated powder was fed in areceiving funnel of the vertical rectangular chute joined up with avibrating system which serves for pre-compaction of said

16 mechanically alloyed alloy powder to obtain a density of 1.6-1.8g/cm³ and transportation of the powder from top downwards. The verticalchute traverses the furnace for heating of the powder and maintenance ofthe desired temperature up to 500° C. Then from the funneled opening ofthe chute the hot pre-compacted

16 alloy powder is fed in a receiving bin of the rolling mill with adesign opening between the rolls and a preset rolling speed. The openingin the yield elongation zone is 6 mm. All plant items wherein the powderis transported ensure synchronous continuous feeding of the mixture tothe rolling mill and maintain regularity of volume, weight andtemperature variables of the production process. When the hot powder isfed in the closed space of the yield elongation zone at a temperature of430-470° C. and under a specific pressure from 300 up to 600 MPa, hotcompaction takes place (relative density is 0.98-0.99). A 300 kg sheetwas continuously produced in the rolling mill. The hot-compacted sheetwas cut to blanks of 1000×120×6 mm in size. Some first hot-compactedblanks were fed for free foaming. These blanks were placed in the forms,sizes of which corresponded to those of the blanks (1000×120-200×27 mm),with walls made of heat-insulating material and were subjected tohigh-temperature treatment at a temperature of 760° C. When atemperature of a hot-compacted blank exceeded that of solid-liquid phasetransformation, the foaming of this powder blank began and when aluminumlayer appeared above the form wall of 27 mm in height, termination ofthe foaming was evaluated visually. The form was taken out of thefurnace and the foamed blank was cooled down intensively. Size of theporous semiproducts was 1000×120-200×28.5 mm. Bottom surface of theporous plate was smooth, while the top surface had indications of swellsbecause of internal pores. Side surfaces of the foamed plate weresmooth. Density of the porous plates produced was 0.58-0.61 g/cm³.Porous semi-product yield was 100%.

[0065] The second part of the hot-compacted blanks of 1000×120-200×6 mmin size was foamed in the same heat-insulating material forms at atemperature of 760° C. and after appearance of aluminum edge above theform wall of 27 mm in height termination of the foaming process wasevaluated visually. The form was transferred from the furnace in itstechnological space with lower temperature, wherein the plate with asmooth surface was put on the end of the form and after fixation of thesmooth surface the plate was taken away, the form was taken out of thefurnace and the foamed semiproduct was cooled down intensively. Size ofthe porous semiproducts produced was 1000×120-200×27.5 mm. In this case,top and bottom surfaces of the porous plates were smooth. Side surfacesof the foamed plates were smooth as well. Density of the poroussemi-products produced was 0.60-0.63 g/cm³: Porous semiproduct yield was100%.

EXAMPLE 3

[0066] The example of the realization of the method for production offlat hot-extruded semiproducts from grinded particles of varioussecondary aluminum alloys in the rolling powder mill is as follows.

[0067] Aluminum alloy particles of 1.0-4.5 mm in size, produced bygrinding of

16 Al—Cu—Mg—Mn alloy scrap (a liquidus temperature of the alloy is640-645° C., a temperature of formation of equilibrium low-melting pointeutectic is 505-510° C.) of 300 kg in weight were filled in a bin. Then,using a special measuring machine, the

16 aluminum alloy grinded particles were spread on a belt conveyer ofthe heating furnace as a uniform layer with a bulk weight of 1.30-1.36g/cm³. The particles were heated in the furnace under nitrogenatmosphere at a temperature of 500-550° C. The heated particles were fedin a receiving funnel of the vertical rectangular chute joined up with avibrating system. The particles filled the whole volume of the verticalbin full and passing a zone of the vertical chute joined up with avibrating system they were pre-compacted to obtain a green density of1.6-1.7 g/cm². Simultaneously the pre-compacted particles passing thevertical chute were heated up to 500-550° C. Then the hot

16 alloy particles were fed in a receiving bin of the rolling mill andthen in the design opening between the rolls which governed the arc ofcontact of the rolling mill. The arc of contact of the rotating coldrolls pulled the hot particles in the yield elongation zone wherein apartial cooling and consolidation of the particles and compaction ofthem with a degree of deformation from 5 up to 10% took place. Theopening in the yield elongation zone was 6 mm. Thickness of the sheetproduced from grinded

16 alloy particles was 6 mm. All plant items wherein the particles weretransported ensured synchronous continuous feeding of the particles tothe rolling mill and maintained regularity of volume, weight andtemperature variables of the production process. When the cooled butstill rather hot

16 alloy particles are fed in the closed space of the yield elongationzone at a temperature of 430-450° C. and under a specific pressure from300 up to 600 MPa, hot continuous compaction or extrusion takes place(relative density is 0.97-0.99). The

16 alloy particles up to 300 kg in weight were continuously deformed inthe rolling mill to sheet product. The hot-compacted sheet was cut toblanks at the shears behind the rolling mill. As a result of continuoushot compaction conditions, a continuous sheet from

16 alloy particles was produced and was cut to 1000 mm lengths at theshears.

EXAMPLE 4

[0068] The example of the realization of the method for production ofaluminum-clad hot-extruded sheets from grinded particles of variousaluminum alloy scrap in the rolling mill is as follows.

[0069] Aluminum alloy particles of 1.0-4.5 mm in size, produced bygrinding of

16 Al—Cu—Mg—Mn alloy scrap (a liquidus temperature of the alloy is640-645° C., a temperature of formation of equilibrium low-melting pointeutectic is 505-510° C.) of 300 kg in weight were filled in a bin. Then,using a special measuring machine, the

16 aluminum alloy grinded particles were spread on a belt conveyer ofthe heating furnace as a uniform layer with a bulk weight of 1.30-1.36g/cm³. The particles were heated in the furnace under nitrogenatmosphere at a temperature of 500-530° C. The heated particles werefilled on moving hot aluminum sheets (450° C.), thickness and width ofthe sheets being 1 and 120 mm respectively. Prior to it the coiledaluminum sheets traversed a heating device wherein said sheets wereheated up to 450° C., then they entered a receiving funnel of thevertical rectangular chute and were pressed against its walls inside.Thus, contact of the moving sheets with walls of the vertical chutejoined up with a vibrating system was carried out. Then the aluminumsheets were pulled through a receiving bin of the rolling powder milland fed in the yield elongation zone of the rolls, wherein the width ofthe hot-extruded sheet was formed. Sheet ends leaving the rectangulargroove of the rolls were folded edgewise to produce a seam. When theline of the cladding sheets was mounted, hot 116 alloy particles werefilled in a receiving bin and then they were fed in a design openingbetween the aluminum sheets. Then, the

16 alloy particles together with the cladding sheets were fed in areceiving bin of the rolling mill and then in the design opening betweenthe rolls which govern the arc of contact of the rolling mill. Thisopening was constant from the vertical receiving bin up to designopening between cold rolls which govern the arc of contact of therolling mill. The arc of contact of the rotating cold rolls pulled thehot cladding sheets together with the particles in the yield elongationzone wherein a partial cooling and consolidation of the particles andcompaction of them with a degree of deformation from 5 up to 10% tookplace. The particles filled the whole space between the sheets to theentire length of them from the vertical receiving bin up to the seamunder the rolls and passing a zone of the vertical chute joined up witha vibrating system they were pre-compacted to obtain a green density of1.6-1.7 g/cm². Simultaneously the pre-compacted particles passing thevertical chute were heated up to 500-530° C. When the space between thecladding aluminum sheets was filled with the particles, the rolling milland all sinchronized particle feeding system were started up. Theopening in the yield elongation zone was 6 mm. Thickness of the claddingaluminum sheet was 1 mm. Thickness of the sheet produced from grinded

16 alloy particles was 4 mm. The design space between the claddingsheets ensured plastic deformation of 5%. The opening between the rollswhereto the receiving bin of the rolling mill enters should be increasedby a thickness of the two aluminum sheets. All plant items wherein theparticles were transported ensured synchronous continuous feeding of theparticles to the rolling mill and maintained regularity of volume,weight and temperature variables of the production process. When thecooled, but still rather hot (450° C.) particles are fed in the closedspace of the yield elongation zone under a specific pressure from 300 upto 600 MPa, hot continuous compaction takes place (relative density is0.98-0.99). The

16 alloy particles up to 300 kg in weight were continuously deformed inthe rolling mill to sheet product. The hot-extruded clad sheet was cutto blanks at the shears behind the rolling mill. As a result ofconditions of continuous extrusion of the aluminum-clad

16 alloy particles, a continuous sheet up to 120 mm in width wasproduced and cut to 1000 mm length at the shears. In the end,

16 alloy sheets clad with 1 mm thick aluminum layer on both sides wereproduced. Thickness of the cladding aluminum or aluminum alloy can bechosen from 0.3 up to 1 mm and more.

[0070] A temperature of heating of the aluminum alloy particles prior torolling to obtain standard properties of an alloy prepared frominexpensive grinded scrap should correspond to hard plastic state, i.e.be below that of low-melting point eutectic formation by 20-50° C. Inaccordance with the present invention, the recommended high temperaturesof alloy particle heating, which exceed those of low-melting pointeutectic formation are caused by the main condition, namely the coldrolls with which the rolling process always begins. Therefore,overheating of the particles fed in the rolling mill allows one, in thefirst place, to produce the hot-extruded sheets with desired properties,with the clad layer or without it. In the second place, when theoverheated particles are fed between the rolls of the rolling powdermill, the surfaces of the rolls are heated due to heat transfer from thebulk of the particles under rolling. Even in the case of heating of theroll surfaces up to 150° C., temperature gradient between a rolltemperature and a temperature of the heated particles reduces. To obtaina particle temperature of 450° C. in the yield alongation zone, atemperature of heating of the particles in the furnace can be reduceddown to 500° C. This temperature does not cause formation of liquidphase in the form of low-melting point eutectic in the alloy particlesand ensures conduct of the hot compaction process when new structuralconditions arise in the particles.

[0071] Therefore, for creation of optimum conditions for conduct of theprocess, both for powders and particles, with economically andtechnically attractive indices, the rolling should be carried out withthe use of plastic one-phase alloy scrap overheated up to 600° C. forheating of the rolls at the initial stage. When roll surfaces wereheated up to 100-150° C., chemical composition of the fed material waschanged on the furnace conveyer, for example, powder were filled, and atemperature was controlled in a range of 490-500° C. rather than500-530° C. Intensity of TiH₂ decomposition reduces already at thesetemperatures, while properties of the hot-compacted sheets are keptcompletely, as compaction is carried out at optimum temperatures of430-460° C.

[0072] As a result, in case of the properly chosen process parameters,the dense continuous hot-compacted sheets made from powders andhot-extruded sheets made from grinded particles are formed with relativedensity and thickness being 0.97-0.99 and from 3.0 up to 10 mmrespectively.

[0073] The described examples of the realization of the invention inaccordance with all variants of the method ensure the possibility of therealization of the invention and attainment of the above-mentionedtechnical results in all cases which solicited scope of protection isspread to, but they do not exhaust all potentialities of the realizationof the invention characterized by the set of signs shown in the claim.

1. A method for production of porous semiproducts from aluminum alloypowders, including mixing of an aluminum alloy powder with porophoresshowing a decomposition temperature above that of aluminum powdermelting, filling of a mixture produced in a mould, heating of said mouldfilled with said powder mixture under inert gas atmosphere, hotcompaction, cooling, rolling to sheet, cutting of the sheet to blanks,placement of said blanks in a form with heat-insulating material walls,high-temperature treatment to conduct the foaming process at a liquidustemperature of the powder alloy and repeated cooling. The methoddiffered from the prior art by the fact that during mixing of analuminum alloy powder with porophores, oxide and hydroxide powderadditions from 1 up to 10% are made in the mixture, as well as grindedsecondary aluminum alloy particles of 0.5-4.5 mm in size and mixing withsaid particles is carried out in an attritor for production of amechanically alloyed powder alloy and after heating a powder mixtureproduced is filled in a vertical mould which ensures simultaneousvibratory compaction and maintenance of a temperature of said powdermixture which is fed in a rectangular groove of a rolling mill toconduct continuous hot compaction in a closed groove formed byhorizontal rolls at a temperature of 430-500° C. provided that thefollowing conditions are observed: H=h×γ×α, where H is an openingbetween the rolls along the arc of contact, mm: h is a thickness of theproduced sheet, mm; γ is a powder compaction coefficient; α is anexperimental coefficient, where 1.5≧α≧4.5.
 2. A method as defined inclaim 1, differed by the fact that after termination of the foamingprocess the form with heat-insulating material walls is placed in atechnological space of a furnace with lower temperature and forformation of upper smooth surface, a smooth heat-insulating materialplate which does not react with molten aluminum is put on the end of theform. Then the form is taken out of the furnace, the plate is taken awayand the upper smooth surface of the semiproduct produced is cooled downintensively.
 3. A method as defined in claim 1, differed by the factthat the heat-insulating material which does not react with moltenaluminum is made with embossed surface which forms a replicatedimpression on the solidifying aluminum surface.
 4. A method as definedin claim 1, differed by the fact that prior to heat treatment, a stampedsheet is placed on the bottom of the form and a blank is placed on saidsheet. After placement of said from in a technological space of thefurnace with lower temperature the heat-insulating material plate whichdoes not react with molten aluminum and made with embossed surface isput on the end of the form to produce replicated impression on the upperaluminum surface. Then the form is taken out of the furnace, the plateis taken away and the upper surface of the semiproduct produced iscooled down intensively.
 5. A method as defined in claim 1, differed bythe fact that instead of aluminum powder use is made of grinded scrap ofaluminum alloy semiproducts both extruded and rolled ones, made fromsoft aluminum alloys A

O, A

1 and wrought alloys AM

, A

31, A

33, AM

3,

16, as well as copper, plastic metals and alloys, with particle sizebeing from 0.5 up to 4.5 mm.
 6. A method as defined in claim 1, differedby the fact that in case of mixing of an aluminum alloy with porophoresin the attritor, use is made of grinded particles of aluminum alloys andcopper and other plastic metals with size fractions of 0.5-2.5 mm,1.0-3.0 mm, 1.5-4.5 mm.
 7. A method as defined in claim 1, differed bythe fact that when grinded scrap of aluminum alloys A

O, A

1 and hard wrought alloys AM

, A

31, A

33, AM

3, AM

5,

16 are mixed in the attritor, additions of a porophore are made togetherwith additions of refractory particles of aluminum oxide, boron carbideand silicium carbide, with a range of size being 5-100 μm.
 8. A methodas defined in claim 1, differed by the fact that when grinded scrap ofaluminum alloys is mixed in the attritor, additions of refractoryintermetallics particles, for example, NiAl3, NiAl, Cr2Al6 and otherswith a range of size being 10-100 μm are made in the mixture.
 9. Amethod as defined in claim 1, differed by the fact that for a reductionin thickness of a sheet to be produced during hot compaction, a powdermixture is fed between moving steel sheets passed by the vibrating chutein the grooved rolls of the rolling mill.
 10. A method as defined inclaim 9, differed by the fact that during hot compaction of a powdermixture, cladding of the compact with steel or titanium sheets can becarried out due to feeding of said powder mixture between the moving hotsheets passed by the vibrating chute in the grooved rolls of the rollingmill with subsequent folding of ends of the sheets for formation of aseam. In this case also, some proportions for filling of said powdermixture are specified and a temperature of said powder mixture in theyield elongation zone should be increased up to 500-520° C., with degreeof deformation being 2-5%.
 11. A method as defined in claim 9, differedby the fact that during hot compaction of a powder mixture, cladding ofthe compact with aluminum sheets can be carried out due to feeding ofsaid powder mixture between the moving hot sheets passed by thevibrating chute in the grooved rolls of the rolling mill with subsequentfolding of the ends of the sheets for formation of a seam. In this casealso, some proportions for filling of said powder mixture are specifiedand a temperature of said mixture in the yield elongation zone should bemaintained up to 430-450° C.
 12. A method as defined in claim 1,differed by the fact that during hot compaction of a powder mixture,pack cladding is carried out via feeding of packs with cladding sheets,for example, from titanium or steel, heated under inert gas atmosphere,with prepared surfaces being in contact with each other and with awelded front end of a pack in the groove of the rolling mill, withdeformation being from 3 up to 15%.
 13. A method as defined in claim 1,differed by the fact that due to a difference in the degree of blacknessof the form wall and aluminum and appearance of light belt of aluminumabove the form wall during foaming of a product, termination of theforming process can be determined visually.